1. Field of the Invention
The present invention relates to a speed control system for a motor vehicle having an internal combustion engine with electronically controlled fuel injection equipped with a turbocharger and, more particularly, to an improvement in a vacuum actuator controlling a throttle valve to constantly maintain a selected speed of the motor vehicle.
2. Description of the Prior Art
A conventional speed control system for a motor vehicle includes an internal combustion engine with a turbocharger and an electronically controlled fuel injector and is disclosed for example in U.S. Pat. No. 4,227,372 granted on Oct. 14, 1980 to Kakimoto et al.
Such a conventional speed control system merely limits the maximum vehicle speed to a desirable level but provides no controlling of the throttle valve.
It is well known in the art that a compressor wheel in a turbocharger of an internal combustion engine can include electronically controlled fuel injectors disposed between the air cleaner and the throttle valve to pressurize intake air inducted into the intake manifold. As a result, the vacuum pressure caused at the intake manifold is greatly decreased upon the compressor wheel being driven.
Accordingly, a vacuum actuator operated by vacuum pressure generated at the intake manifold cannot control the throttle valve due to shortage of vacuum pressure.